Design and mechanistic insights into ZMF59/CpG: a complementary adjuvant system boosting immunity and safety in herpes zoster vaccines

The recombinant herpes zoster (HZ) vaccine, Shingrix®, faces challenges such as high reactogenicity and manufacturing complexities of AS01 adjuvant, highlighting the need for safe and effective alternatives. In this study, we developed and evaluated four emulsion-based adjuvant systems (ZMF59/QS-21, ZAS03/QS-21, ZMF59/CpG, and ZAS03/CpG) for HZ vaccines in a varicella-zoster virus (VZV)-primed mouse model. Mechanistic studies were conducted at the molecular, cellular, and tissue levels using fluorescence imaging, flow cytometry, and Luminex assays. We found that although ZAS03 alone elicited higher antibody titers than ZMF59, ZMF59/QS-21 was superior to ZAS03/QS-21, and ZMF59/CpG also tended to elicit higher responses than ZAS03/CpG. Notably, ZMF59/CpG induced robust humoral and cellular immune responses comparable to the AS01-like adjuvant, while avoiding safety concerns related to excessive immune activation in emulsion-based QS-21 formulations. Synergy analysis indicated that these enhancements of ZMF59/CpG were driven predominantly by additive and complementary effects, with synergy restricted to some long-term adaptive indicators. Mechanistically, ZMF59/CpG enhanced antigen retention and established a robust, Th1-polarized immune microenvironment at the injection site, which boosted recruitment of neutrophils, T cells, and monocytes, the latter differentiating into monocyte-derived dendritic cells. The enhanced recruitment improved antigen uptake and facilitated more efficient delivery to draining lymph nodes. Notably, the ZMF59/CpG-adjuvanted HZ vaccine has been approved for human clinical trials by the Center for Drug Evaluation of the China National Medical Products Administration. These results highlight ZMF59/CpG as a promising clinical candidate and provide valuable insights into the development of adjuvanted vaccines with broad implications for vaccine design.